1. Field of the Invention
The present invention relates to a metallic core wiring substrate, and particularly to a metallic core wiring substrate which is suitable for manufacturing printed wiring used for packaging required components at a high density or for a hybrid integrated circuit (HIC).
2. Description of the Prior Art
A conventional metallic core wiring substrate which has been widely sued heretofore is manufactured by applying an insulating layer to the surface of a metallic plate to form a core, and additional steps are performed to define the required electrically conductive patterns, through holes or the like on the insulating layer. Accordingly, there is a disadvantage in that the manufacturing process is complicated with the result that the products become expensive. In order to eliminate the above described disadvantage, there has been proposed a method wherein a printed board is directly bonded to the surface of a core metal and components are then packaged on the printed board. However, with a construction according to the above method wherein circuit patterns are formed on the back of the surface of the printed board joined with the core metal) of the printed board, and the circuit patterns are connected with components to be packaged on the surface of the printed board via through holes in order to increase the density of the components it is difficult to maintain the insulation between the components and the circuit patterns on the back of the printed board. Hence, the above described construction is hardly accepted, and furthermore, it involves a disadvantage in that separate lead terminals must be further attached to the printed boards if the provision of the lead terminals is required. Furthermore, since a pad is used at the connection between the lead terminals and the wiring patterns, the space for packaging the components is narrowed by a width of the pad in the above described construction, so that it cannot satisfy the requirement for miniaturization of the electronic circuit.
It has been heretofore common to employ a ceramic sheet or a plastic laminate as the substrate for manufacturing a hybrid IC. However, such a ceramic sheet itself is expensive, and in addition, a silver-palladium paste is required for forming electrically conductive patterns on the sheet, so that the resulting product becomes more expensive. In addition, when it is intended to utilize both surfaces of the ceramic substrate in order to elevate a wiring density, through holes are necessary and the processing therefor is considerably troublesome.
On the other hand, the latter substrate, i.e. a plastic laminate, does not involve the problems as mentioned above, but a step for connecting lead terminals with the laminate is required in order to secure them in this case also so that considerable time is necessary therefor. Furthermore, in the case where a metallic core printed circuit is vertically connected to a mother board through these lead terminals, the printed circuit provided upright becomes higher by a height corresponding to a stationary part of lead terminals. Thus, there is a particularly disadvantageous drawback for the case where there is a severe requirement for the miniaturization of electronic circuit.
It is an object of the present invention to eliminate the disadvantages involved in the conventional metallic core wiring substrates as mentioned above, particularly the disadvantages of a decrease in a packaging density for the components and an increase in a height of the lamination. Another object of the present invention is to provide a metallic core wiring substrate which makes a connection between an electronic circuit provided on the substrate and lead terminals easy and solves a problem in a case involving further connection thereof with another printed circuit.